K.R. Matthews

Comparative evaluation of Vitek Gram-positive identification system and API Rapid Strep system for identification of Streptococcu species of bovine origin

The Vitek Gram-positive identification system (GPI, Vitek Systems, Inc., Hazelwood, MO) and the API Rapid Strep system (Analytab Products, Plainview, NY) were evaluated for species identification of streptococci isolated from bovine mammary glands and compared to conventional biochemical methods. A total of 144 strains including Streptococcus uberis (60), S. dysgalactiae (32), S. agalactiae (15), S. bovis (15), Enterococcus faecium (10) and Ent. faecalis (12) were evaluated. All reference strains were identified correctly by both systems. Vitek GPI card system identified 94.4% of strains, including 95% of S. uberis, 93.8% of S. dygalactiae, 93.3% of S. agalactiae and S. bovis II, 90% of Ent. faecium and 100% of Ent. faecalis. Majority of strains were identified with a 90-99% level of confidence, with an average of 8 h needed for identification. The API Rapid Strep system identified 96.5% of strains correctly, including 95% of S. 96.9% of S. dysgalactiae, 93.3% of S. agalactiae, and 100% of S. bovis II, Ent. faecium, and Ent. faecalis. Majority of strains were identified with excellent level of identification. With the exception of S. uberis, most strains were identified at 4 h of incubation.

Encapsulation of Streptococcus uberis: Influence of storage and cultural conditions

Streptococcus uberis (n = 100) isolated from bovine mammary secretions were assessed by India ink for expression of capsule. Organisms were evaluated under four conditions; (1) after primary culture on blood agar, (2) following 5 passages on blood agar, (3) after 5 passages in Trypticase Soy Broth (TSB), and (4) after storage in 10% skim milk. Strains from primary culture (44 of 100) were positive for an unstained halo (capsule) by the India ink method. Number of strains expressing capsule decreased greatly after passage and following storage. Freeze-etching followed by electron microscopy confirmed results of India ink preparations. Strains were also cultured in various media to determine influence of medium components on capsule expression. Todd-Hewitt medium supplemented with either serum or egg yolk enhanced the size of capsule expressed. Results of this study may aid researchers investigating the pathogenicity of S. uberis.